In a so-called drum type (or a front loading type) spin extractor, wet laundry after being washed is loaded into a basket drum having a horizontal rotation axis from the front opening, and the drum is rotated about the horizontal axis at high speed. When, in the spin extractor of this type, the drum is rotated at high speed with the laundry distributed unevenly on the inner peripheral wall of the drum, abnormal vibration occurs due to the uneven mass distribution around the axis, causing an abnormal noise.
Several proposals have been made addressing this kind of abnormal vibration of the drum type spin extractors. In the Publication No. H6-254294 of Japanese Unexamined Patent Application, for example, a spin extractor is disclosed in which the laundry is evenly redistributed on the inner peripheral wall of the drum by rotating the drum at low speed before rotating it at high speed for extraction. The process in detail is as follows. First, the drum is rotated at a low speed for a very short time (at a speed corresponding to the centrifugal force of 1.2-1.5 G on the wall of the drum for about 5 seconds, for example). Next, the drum is rotated at another low speed which is a little higher than said low speed but much lower than the high speed for liquid extraction (at a speed corresponding to 2.3-2.6 G of the centrifugal force for 20 seconds, for example). The publication shows that the laundry in the drum is redistributed by such two-stage balancing operation. In addition, the spin extractor is provided with a vibration sensor on its base as a means for detecting the eccentric load due to an uneven distribution of the laundry in the drum. When the sensor detects vibration while the drum is rotated at the high speed for extraction, the speed of the drum is reduced.
In the above spin extractor, it is not assured that the laundry is redistributed evenly with a single cycle of the low-speed balancing operation. If vibration is detected by the sensor when the drum is rotated at the high speed for extraction, another trial of the low-speed balancing operation is necessary to redistribute the laundry. Since the difference between the low speed for balancing and the high speed for extraction is very large, it takes a considerable time to change the speed of the drum from one to the other. It takes a long time before a thoroughly even distribution is obtained if such trials are repeated several times.
Further, in the above spin extractor, the drum is rotated at a speed as high as the speed for extraction while detecting the eccentric load. So, when the eccentric load is very large, a motor for rotating the drum is overloaded while detecting the eccentric load, which may cause a breakdown of the motor.
For addressing the above problems, the inventors of the present application proposed a novel spin extractor disclosed in the Publication No. H09-290089 of Japanese Unexamined Patent Application. In this spin extractor, the laundry in the drum is redistributed by a balancing operation as follows. First, the drum is rotated at a speed where the centrifugal force acting on the laundry is a little greater than that of the gravity, so that the laundry is pressed on the inner peripheral wall of the drum and rotates with the drum. Under this condition, the eccentric load due to the uneven distribution of the drum is detected, where the eccentric load is detected based on the fluctuation in the motor current supplied to the drum motor. If the magnitude of the eccentric load is greater than a predetermined allowable value, the speed of the drum is rapidly reduced for a short time at a timing when the eccentric load is at the top of the drum, whereby part of the laundry falls onto the bottom because the centrifugal force decreases at the timing. By the balancing operation, the laundry in the drum is redistributed within a short time, so that the start of the high speed extraction is advanced.
The above spin extractor, however, may fail to suppress the abnormal vibration depending on the quality of the laundry loaded in the drum. Suppose, for example, that the laundry includes two types of articles: one type being such that liquid is hardly extracted, such as a blanket, and the other type being such that liquid is easily extracted, such as a shirt or a blouse (the two types of articles are respectively referred to as "hard-to-extract article" and "easy-to-extract article" hereinafter). In such a case, it is difficult to maintain a desirable load balance throughout the extraction even if the laundry is desirably distributed before the extraction, because the loading state considerably changes as the liquid is extracted from the laundry during the extraction.